Pin seam fabrics for use on papermaking machines are composed of a woven base and the ends of the base are provided with interdigitated loops that are connected by a removable pin or pintle. The base fabric can either be woven in endless form, as disclosed in U.S. Pat. No. 3,815,645, or alternately can be woven in flat form, in which case loops are attached to the free ends of the fabric, in a manner such as disclosed in U.S. Pat. Nos. 4,123,022 and 4,401,137.
A pin seam fabric has distinct advantages in that it can readily be installed and removed from the papermaking machine by insertion and removal of the pin from the interdigitated loops at the ends of the fabric. However, in the past, pin seam fabrics have not been successfully employed as papermaker felts in the press section of the papermaking machine. It is essential that a felt have uniform water drainage characteristics and density throughout its length in order to obtain uniform water extraction from the paper web, as well as to prevent marring or marking of the paper. As pin seam fabrics have generally been produced in flat form with loops subsequently attached or interwoven into the free ends, the density adjacent the ends is normally greater, due to the interweaving of the loops, than the density of the remainder of the fabric. If used as a felt, this variation in density can produce non-uniform water extraction characteristics, and the added fibers in the area of the pin seam joint can cause marring or non-uniform texture for the paper web.
It is also recognized that it is desirable to construct a papermaker's felt with an outer batt of fibrous material which is needled to the base fabric. The batt serves to engage and protect the paper sheet as it passes through the nip, while the base fabric is designed to receive extracted water from the paper sheet and carry it away from the press nip. The batt is attached to the base fabric on a needling machine, in which the base fabric, in endless form, is advanced through the needling area. However, a needled batt is not normally used with a pin seam base fabric, because the batt, through needling, would be intertwined with the pin seam joint and would prevent the joint from being opened so that the fabric could be installed on the papermaking machine.
U.S. Pat. No. 4,601,785 discloses a pin seam base fabric having a needled batt which can be used as a felt in the press section of a papermaking machine. According to the aforementioned patent, the base fabric is produced in flat form and loops are provided in the ends to provide a pin seam fabric. A batt is then needled into at least one surface of the fabric and after needling, the batt is cut at a location offset from the pin seam joint and the portion of the batt extending across the joint is loosened from the base fabric to provide a flap. The pin is removed from the pin seam joint, and after installation of the felt on the papermaking machine, the pin is reinserted into the interdigitated loops. The loose flap of the batt is then reattached to the base fabric either by needling or adhesives.
While U.S. Pat. No. 4,601,785 describes a manner in which a needled pin seam base fabric can be utilized as a felt in the press section of a papermaking machine, in actual practice, after the batt is loosened, cross direction stuffers or yarns are required to be inserted beneath the flap and behind the loops to fill the gap resulting from the loosening of the batt flap from the base fabric. In addition, when installed on the papermaking machine, it is necessary that the loose flap of the batt be needled, glued, or otherwise reaffixed to the base fabric. The insertion of stuffers along with the reattachment of the flap requires a substantial amount of manual labor.